1. Smell and Taste Smell aka Olfaction (Latin olfacere) Taste aka Gustation (Latin gustare) Minor Senses - Really? Chemical Senses Smell and Taste very closely related to each other

3. Where does smell figure? In humans Strong link to sense of taste Strong link to emotional states Exploited by commercials/marketing Used for identification of gender Pheromones - signal sexual arousal or a readiness for mating

4. Basics: What do you need for smell? Odorous Substance Airborne Perceptual system that can parse or segregate the information in airborne odorant molecules

5. Categorizing Smell Aristotle: Pungent, Succulent, Acid and Astringent Hennings Smell Prism Based on verbal descriptors of smell Multidimensional Scaling (MDS) Subjects rate only the similarity of odor-pairs Consistent arrangement in an N-dimensional space

6. MDS Eugenol (cloves) Methyl Salicylate (cloves) Vanillin Aldehyde C14 (flowers) Nitrobenzene (almonds) Citronelli (lemons) Turpentine Propionic acid (sweaty socks) Acetic acid (vinegar) Scatole (feces) Hydrogen Sulfide (rotten eggs)

7. Physiology Nasal Cycle Olfactory Epithelium Olfactory Receptor Cells (Complete Neurons) Free Nerve Endings Olfactory Nerve (Axons of the ORCs)

8. Physiology contd. Olfactory Receptor Cells have cilia Cilia are bathed in mucous Mucous contains Odorant binding proteins (OBP) OBP transmits the odorant molecules from the air to receptor sites on the cilia

9. Olfactory Pathways

10. Neural Representations Very little known No odorotopic map found. All cells fire for all odors but form different patterns different odors => Population code. Other complications: Change in intensity leads to increase in the firing rate of neurons but triggers changes in the perceived quality of the odorant.

11. Odor Perception Odor (as well as taste) are much more phenomenological than vision or audition. Odor Detection Very good: Mercaptan 1 part per 50 billion parts of air. Varies greatly from odor to odor (molecular properties) Varies with a variety of other factors Time of day, Age and Gender Smoking in injurious to odor detection! Odor Identification Much worse Shows context dependence Varies once again with age and gender

12. Odor Identification Determined by Gender Women vastly superior Can be improved with practise - benefits both genders Stimulus Saliency Infants and mothers can recognize each other by smell alone Infants hedonic reactions to smell develops with age Odor Familiarity - Seen in elderly people Smoking is injurious to odor identification!

13. Some more amazing facts Odor Constancy Natural sniffs lead to constant odor perception but artificial blowing of air does not Common Chemical Sense Odors judged pleasant at moderate concentrations are judged unpleasant at high concentrations Related to the action of free nerve endings - stimulated in an indiscriminate manner Warning system for the organism Adaptation - Adapt to a particular odor Cross Adaptation: Adapt to a different odor Could have led to odor categorization but turns out that cross-adaptation is not symmetric!

14. Disorders of Smell Anosmia or “Odor Blindness” Often caused by a blow to the head Temporary since ORCs can regenerate Sometimes can be total but in that case is specific to certain odors, e.g. sweat, urine Anosmia can have serious consequences such as loss of apetite and weight